The invention relates to a conditioning system and to a method for reducing the oxygen content of water carried in a subsystem of an industrial plant.
Subsystems in which water is carried are provided in a multiplicity of industrial plants, for example, in chemical production workshops or in nuclear or fossil-fuel power plants. Such a subsystem may be, for example, a cooling circuit or a circulating circuit for the working medium.
In such a context, a high oxygen concentration in the water carried in the subsystem may lead to a corrosion of fittings or of pipes of the subsystem. To avoid damage to the subsystem or else to the entire industrial plant reliably, therefore, it may be necessary, as required, to reduce the oxygen content of the water carried in the subsystem. The requirement may arise, in particular, when the water is subjected continuously to oxygen for operational or conceptual reasons.
For example, it may be necessary for the intermediate cooling circuit of a nuclear plant to have a compensating tank for the water carried in the intermediate cooling circuit, the water coming into contact with ambient atmosphere in the manner of an open configuration in the interior of the tank. The continuous introduction of oxygen into the intermediate cooling circuit caused thereby may lead to an oxygen concentration in the water carried there of, for example, up to 8 ppm (parts per million). For reasons of corrosion protection, however, it may be necessary, in spite of the continuous introduction of oxygen, to keep the oxygen content in the water carried in the intermediate cooling circuit permanently at a value of less than 20 ppb (parts per billion).
For such a purpose, in an intermediate cooling circuit of a nuclear plant, there normally is a provision for an on-demand feed of the water carried there with hydrazine (N2H4). The hydrazine reacts with the oxygen contained in the water to form nitrogen (N2) and water (H2O), so that the oxygen content of the water is lowered significantly. However, precisely in the case of a plant with continuous oxygen introduction, a more or less permanent addition of hydrazine is necessary, so that more and more nitrogen is formed in the water. The additional formation leads to a continuous rise in the conductivity of the water and, therefore, to a permanent change in the water chemistry. At the same time, for operational reasons, when predetermined conductivity limits are exceeded or when a predetermined PH value is exceeded, a complete exchange of the water carried in the respective subsystem of the industrial plant is necessary. Precisely where complex industrial plants are concerned, a complete water exchange is highly complicated and, moreover, entails undesirably long standstill times of the plant.
Alternatively, on-demand vacuum degassing of the water may be provided to set a low oxygen content in the water. Such a concept, however, involves a high outlay, particularly in terms of the components required.
It is accordingly an object of the invention to provide a conditioning system and method for reducing the oxygen content of water carried in a subsystem of an industrial plant that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that makes it possible, at particularly low outlay in structural and technical terms, to have a reliable on-demand setting of the oxygen content in the water below a predeterminable limit value.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a conditioning system for reducing an oxygen content of water carried in a subsystem of an industrial plant, including an electrolysis unit having a hydrogen side, an anode, and a cathode, the anode and the cathode connected to the subsystem to decompose water into hydrogen and oxygen, and a hydrogen/oxygen recombination catalyst connected to the subsystem, the hydrogen/oxygen recombination catalyst following downstream the anode and the cathode on the hydrogen side.
The invention relates to a treatment system for reducing the oxygen content of the water that is guided in a subsystem of a technical installation. The aim of the invention is to provide a reliable way of adjusting the oxygen content of the water below a predetermined limit value, as required. The invention strives to be as simple as possible in constructional and technical terms. To such an end, an electrolysis unit for decomposing a portion of the water into hydrogen H2 and oxygen O2 is connected to the subsystem. A hydrogen-oxygen recombination catalyzer that is connected to the subsystem is connected downstream of the electrolysis unit on the hydrogen side.
The invention achieves its objectives, with respect to the conditioning system, by connecting an anode and cathode of an electrolysis unit to the subsystem to decompose water into hydrogen and oxygen. They are followed downstream on the hydrogen side by a hydrogen/oxygen recombination catalyst connected into the subsystem.
The invention proceeds from the notion that a reliable setting of a low oxygen content in the water is possible at particularly low outlay by subjecting the oxygen to a reaction, the products of which not adversely changing the water chemistry. Oxygen is recombined with hydrogen, in which the sole final product is water. Feeding with hydrogen as a reaction partner for the oxygen takes place on demand through the electrolysis unit, followed by the hydrogen/oxygen recombination catalyst to ensure a complete conversion of the hydrogen fed therein.
Expediently, the electrolysis unit is provided for decomposing a partial quantity of the water carried in the subsystem and, for such a purpose, is likewise connected on the inlet side to the subsystem. Water from the subsystem can be supplied to the anode and cathode of the electrolysis unit. The terms xe2x80x9canodexe2x80x9d and xe2x80x9ccathodexe2x80x9d as used herein also refer to a plurality of anodes and cathodes. The electrolysis unit may, at the same time, particularly for compensating volume losses, be capable of being fed additionally with water from a separate water reservoir in which the water can be kept, for example, as deionized water.
At the same time, in a particularly advantageous refinement, the hydrogen/oxygen recombination catalyst includes, as catalytically active components, a number of polymer beads provided with a palladium layer, such as are described, for example, in a prospectus from the Bayer company titled xe2x80x9cKatalytische Entfernung von gelxc3x6stem O2 aus Wasserxe2x80x9d [xe2x80x9cCatalytic removal of dissolved O2 from waterxe2x80x9d], No. OC/I 20 377, October 1995.
In accordance with another feature of the invention, the electrolysis unit includes a number of membrane-type electrolysis cells. In such a membrane-type electrolysis cell, the functional principle of a fuel cell, such as is disclosed, for example, from the paper xe2x80x9cBrennstoffzellen fxc3xcr Elektrotraktionxe2x80x9d [xe2x80x9cFuel cells for electrotractionxe2x80x9d], K. Straxcex2er, VDI-Berichte [VDI Reports], No. 912 (1992), page 125 ff., is reversed. Water is supplied to a membrane disposed between an anode and a cathode. By applying a supply voltage between the anode and the cathode, the water is decomposed electrolytically into hydrogen and oxygen. Such a membrane-type electrolysis cell is distinguished by a particularly compact form of construction, so that an electrolysis unit with a number of membrane-type electrolysis cells can be accommodated in a particularly confined space. Consequently, the an electrolysis unit can be connected into the subsystem in a particularly flexible way and so as to be adapted to the specific needs of the subsystem.
In an advantageous refinement, a discharge system for oxygen is connected to the electrolysis unit. Particularly, the electrolysis unit has an oxygen side, and the oxygen discharge system is connected to the oxygen side of the electrolysis unit. Thus, the oxygen generated during the decomposition of the partial quantity of water can be discharged or supplied for another use in a particularly simple way.
In accordance with an added feature of the invention, the electrolysis unit has an inlet side and an outlet side. Advantageously, the electrolysis unit is connected into a branch line connected on the inlet side and the outlet side to the subsystem. The partial stream of the water carried by the branch line and, therefore, the feed of the electrolysis unit with water to be decomposed, can be adapted in a particularly flexible way to the hydrogen quantity to be generated, without the occurrence of significant adverse effects on the main water stream circulating in the subsystem. Particularly due to the high effectiveness of the electrolytic decomposition of the partial quantity of water, the branching ratio selected between the partial stream of water carried by the branch line and the main stream of water carried in the subsystem may be comparatively low. To reduce the oxygen content of water carried in an intermediate cooling circuit of a nuclear plant from about 8 ppm to less than about 10 ppb, there may be, at the same time, a leading of only a partial stream of about 10 liters per hour through the branch line, in the case of a water stream of, for example, about 300 liters per hour carried in the intermediate cooling circuit.
In such a configuration, to achieve a particularly homogeneous distribution of the generated hydrogen in the main stream of water and, therefore, particularly high efficiency in the subsequent catalytic recombination, in a further advantageous refinement, the branch line issues on the outlet side into the subsystem in a static mixer.
For an on-demand and, therefore, particularly accurate generation of the hydrogen provided for reducing the oxygen content, the electrolysis unit is expediently assigned a set-point transmitter connected on the input side to a measuring probe for determining the oxygen content of the water. The measuring probe may be connected into the subsystem or else into the branch line. The set-point transmitter advantageously acts on a voltage source provided for supplying voltage to the electrolysis unit. Thus, the generation of the hydrogen can be carried out based on an actual value of the oxygen content in the water and, therefore, particularly on demand.
To check reliably the effectiveness of the catalytic recombination and, therefore, of the reduction in the oxygen content, the hydrogen/oxygen recombination catalyst is advantageously followed in the subsystem by a further measuring probe for determining the oxygen content of the water.
With the objects of the invention in view, there is also provided a method for reducing an oxygen content of water carried in a subsystem of an industrial plant, including the steps of electrolytically decomposing water from a subsystem of an industrial plant into hydrogen and oxygen, and using the hydrogen generated at the same time for recombining the oxygen contained in the water.
The method according to the invention achieves it objectives by decomposing water from the subsystem electrolytically into hydrogen and oxygen and using the hydrogen generated at the same time for recombining the oxygen contained in the water. In particular, a partial quantity of the water from the subsystem is decomposed. The water from the subsystem is supplied both to the anode and to the cathode of the electrolysis unit.
For an on-demand and, therefore, particularly flexible reduction in the oxygen content, the electrolytic decomposition of the partial quantity of the water from the subsystem is advantageously controlled by a measurement value characterizing the oxygen content of the water.
In accordance with a concomitant mode of the invention, water is branched off from the subsystem, is led through an electrolysis unit, and, together with hydrogen generated as a result of the decomposition of the water, is fed back into the subsystem. As much hydrogen as is required for recombining the oxygen contained in the water of the subsystem is generated in the electrolysis unit and is characterized by the measurement value.
The advantages achieved by the invention are, in particular, that a reliable reduction in the oxygen content in the water is ensured by the water being fed with hydrogen and by the subsequent catalytic recombination, a change in the water chemistry being reliably avoided even during continuous operation. Moreover, the on-demand generation of hydrogen in the electrolysis unit ensures, in a simple way, that the hydrogen is supplied to the subsystem without complicated measures for keeping a hydrogen reservoir being necessary. Corrosion of components connected into the subsystem is, therefore, reliably avoided in a simple way, and, in particular, there is also no need for a frequent complete exchange of the water carried in the subsystem.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a conditioning system and method for reducing the oxygen content of water carried in a subsystem of an industrial plant, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.